8 OUTLINES OF EQUINE ANATOMY. 



produced by division of one cell, but tbe cells in temporary 

 cartilage are more evenly diffused througb the mass. 

 Another form of cartilage is found in the foetus, which is 

 termed cellular, since it consists of cells collected together 

 with no apparent intercellular substance. 



Bones are composed of compact and cancellated structure. 

 The former is the dense external layer which they present. 

 In the cancellated, which is situated more internally, the 

 bony structure is arranged in a trabeculated manner, 

 whereby spaces are left which are termed cancelli. Small 

 near the compact substance, these gradually increase in 

 size until in the centre of the bone we frequently find a 

 large open space or medullary canal, so named from its 

 containing the medulla or marrow, a greasy substance, 

 which in the young subject is of a red colour, but in the 

 adult yellow ; it consists of areolar tissue, in the meshes of 

 which are fat and peculiar cells (or myeloplaxes) ; it also fills 

 the cancelli. 



The intimate structure of bones is complex ; through its 

 substance run canals for blood-vessels, and arranged con- 

 centrically around these canals are bony layers termed 

 lamince, between which at intervals are irregular spaces 

 containing the special cells of bone, or lacunce. From each 

 of these lacunae, towards the central or Haversian canal, 

 and towards the other lacunae, run minute passages or 

 canalicuU, through which only the fluid portion or nutritive 

 plasma of the blood is supposed to pass. An arrangement 

 such as that just described is termed an Haversian system, 

 and the Haversian canal of one system is frequently 

 brought into communication with that of another by means 

 of a transverse branch, all the Haversian systems com- 

 posing a bone are not uniform in size. 



Bones are of three kinds, long, flat, and irregular. Long 

 bones (or long round bones), as the femur, radius, &c., have 

 one axis (as a rule) much longer than the others and have 

 a distinct medullary canal. They present a central ossific 

 centre or diaphysis forming the body of the bone, and at 

 each end of this an epiphysis forming an extremity. From 

 either part processes or apophyses may j^roject. Their 

 Haversian canals run parallel to the long axis of the bone, 

 and the different Haversian systems are connected together 

 by connecting laminae, which are concentric with the medul- 

 lary canal of the bone. 



